The present invention relates to pneumatic hand tools and more particularly to pneumatic hand tools having user operated control valves for governing the flow of operating air to the tool.
Pneumatic hand tools having an air powered motor with a user-operated control valve for governing the flow of operating air to the motor are known. Among the various tools that fall within this category are, for example, drills, grinders, meat trimming knives, and skiving, or skinning knives. The knives are used in the meat industry and feature rotating, or oscillating blades that are driven by air motors. Conventionally these tools are connected to a source of high pressure air via a flexible conduit. Their operation is controlled by a user-actuated valve that is opened and closed to start and stop the drive motor.
For safety purposes these tools are often designed so that the user must open the control valve and manually maintain it opened so long as the tool is operated. The valve automatically closes if the user no longer maintains it in its open condition. This minimizes the possibility of tool operation when undesired, which might otherwise result in injury to the user or others. Some tools have handles that house the drive motor and/or the control valve. The user grips the handle and in so doing depresses a valve operating plunger to open the control valve. When the plunger is released the valve closes.
Even though the prior art tools were equipped with control valves of the type referred to, undesired tool operation could sometimes occur. For example, where a tool and/or its source of operating air were improperly maintained, the control valve could be fouled or damaged so that it failed to completely close when the tool was not operating. Consequently, air from the source bled past the valve to the air motor inlet. If the leak has sufficient volume, the air motor will run continuously as long as the air volume remains sufficient. The unintended tool operation was a potential source of workplace injury.
The present invention provides a new and improved pneumatic hand tool that is so constructed and arranged that unintended tool operation is avoided even though the tool motor control valve fails to fully close when the tool is not operating and air from a pressure source bleeds past the valve.
A pneumatic hand tool constructed according to the invention is connected to a source of pressurized operating air and comprises a tool body communicable with the source, a pneumatic motor supported by the tool body, and a control valve for controlling the flow of air from the source to the motor.
The motor has an inlet that is communicable with the source via the control valve so that when the control valve is in an open condition the motor is operated from the pressure source and drives the tool. When the control valve is in its closed condition the motor is not operated.
The control valve comprises a valve body defining a delivery port through which air is supplied to the motor, a seat surrounding the port, and a valving member movable relative to the seat to open and close the port. The valving member is biased toward engagement with the seat to block flow through the port. In its open condition the control valve is stationed relative to the tool body in a first position where the valve body port communicates directly with the motor inlet and the valving member is spaced from the seat so that air from the source is communicated to the motor. In the closed condition the valving member is in a second position where the valving member engages the seat for blocking flow from the pressure source through the control valve and the valve body delivery port communicates with air at ambient atmospheric pressure so that any source air leaking from the control valve delivery port is vented away from the motor inlet passage.
The disclosed control valve body comprises a tubular projecting end that surrounds the delivery port and the tool body comprises a seal member which seals the projecting end when the valve body is in the first position so that the port and the inlet passage are directly communicated. The valve member projecting end is spaced away from the seal member when the valve body is in the second position.
In the disclosed embodiment a spring biases the valving member toward engagement with the seat.
A valving member actuator is fixed with respect to the tool body for unseating the valving member when the control valve is in its open condition.
In an illustrated embodiment a hand grippable lever is provided for enabling a tool user to easily maintain the control valve in its first position. The lever is movable relative to the tool body between a gripped position where the lever maintains the control valve in the first position to a released position where the control valve shifts to its second position.
The illustrated hand tool is connected to the source by a conduit and the control valve is connected to the conduit and extends into a receptacle formed by the tool body.
Additional features and advantages of the invention will become apparent from the following detailed description of an embodiment of the invention and the accompanying drawings that form part of the specification.